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The infrared Hourglass cluster in M8*†
A detailed study of the Hourglass nebula in the M8 star-forming regionis presented. The study is mainly based on recent subarcsec-resolutionJHKs images taken at Las Campanas Observatory andcomplemented with archival Hubble Space Telescope (HST) images andlong-slit spectroscopy retrieved from the European Southern ObservatoryArchive Facility. Using the new numerical code CHORIZOS, we estimate thedistance to the earliest stars in the region to be 1.25 kpc. Infraredphotometry of all the sources detected in the field is given. Fromanalysis of the JHKs colour-colour diagrams, we find that animportant fraction of these sources exhibit significant infrared excess.These objects are candidates to be low- and intermediate-masspre-main-sequence stars. Based on HST observations, the spatialdistribution of gas, dust and stars in the region is analysed. Amorphological analysis of these images also reveals a rich variety ofstructures related to star formation (proplyds, jets, bow shocks),similar to those observed in M16 and M42, along with the detection ofthe first four Herbig-Haro objects in the region. Furthermore, along-slit spectrum obtained with the New Technology Telescope confirmsthe identification of one of them (HH 870) in the core of the Hourglassnebula, providing the first direct evidence of active star formation byaccretion in M8.
| Evolution of X-ray emission from young massive star clusters
The evolution of X-ray emission from young massive star clusters ismodelled, taking into account the emission from the stars as well asfrom the cluster wind. It is shown that the level and character of thesoft (0.2-10 keV) X-ray emission change drastically with cluster age andare tightly linked with stellar evolution. Using the modern X-rayobservations of massive stars, we show that the correlation betweenbolometric and X-ray luminosity known for single O stars also holds forO+O and (Wolf-Rayet) WR+O binaries. The diffuse emission originates fromthe cluster wind heated by the kinetic energy of stellar winds andsupernova explosions. To model the evolution of the cluster wind, themass and energy yields from a population synthesis are used as input toa hydrodynamic model. It is shown that in a very young cluster theemission from the cluster wind is low. When the cluster evolves, WRstars are formed. Their strong stellar winds power an increasing X-rayemission of the cluster wind. Subsequent supernova explosions pump thelevel of diffuse emission even higher. Clusters at this evolutionarystage may have no X-ray-bright stellar point sources, but a relativelyhigh level of diffuse emission. A supernova remnant may become adominant X-ray source, but only for a short time interval of a fewthousand years. We retrieve and analyse Chandra and XMM-Newtonobservations of six massive star clusters located in the LargeMagellanic Cloud (LMC). Our model reproduces the observed diffuse andpoint-source emission from these LMC clusters, as well as from theGalactic clusters Arches, Quintuplet and NGC 3603.
| The star formation region NGC 6530: Distance, ages and initial mass function
We present astrometry and BVI photometry, down to V≃22, of thevery young open cluster NGC 6530, obtained from observations taken withthe Wide Field Imager camera at the MPG/ESO 2.2 m Telescope. Both the Vvs. B-V and the V vs. V-I color-magnitude diagrams (CMD) show that theupper main sequence is dominated by very bright cluster stars, while,because of the high obscuration of the giant molecular cloud surroundingthe cluster, the blue envelopes of the diagrams at V≳14 are limitedto the main sequence stars at the distance of NGC 6530. This particularstructure of the NGC 6530 CMD allows us to conclude that its distance isabout d ≃ 1250 pc, significantly lower than the previousdetermination of d=1800 pc. We have positionally matched our opticalcatalog with the list of X-ray sources found in a Chandra-ACISobservation, finding a total of 828 common stars, 90% of which arepre-main sequence stars in NGC 6530. Using evolutionary tracks of\citet{sies00}, mass and age values are inferred for these stars. Themedian age of the cluster is about 2.3 Myr; in the mass range (0.6-4.0)Mȯ, the Initial Mass Function (IMF) shows a power lawindex x=1.22±0.17, consistent with both the Salpeter index(1.35), and with the index derived for other young clusters; towardssmaller masses the IMF shows a peak and then it starts to decrease.Based on observations made with the European Southern Observatorytelescopes obtained from the ESO/ST-ECF Science Archive Facility.Full Tables 4 and 5 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/430/941
| A Galactic O Star Catalog
We have produced a catalog of 378 Galactic O stars with accuratespectral classifications that is complete for V<8 but includes manyfainter stars. The catalog provides cross-identifications with othersources; coordinates (obtained in most cases from Tycho-2 data);astrometric distances for 24 of the nearest stars; optical (Tycho-2,Johnson, and Strömgren) and NIR photometry; group membership,runaway character, and multiplicity information; and a Web-based versionwith links to on-line services.
| A Deep Chandra X-Ray Observation of the Rich Young Cluster NGC 6530. I. The X-Ray Source Catalog and the Cluster Population
In a deep 60 ks Chandra ACIS X-ray observation of the very young clusterNGC 6530, we detect 884 X-ray point sources and argue that a very largefraction of them (90%-95%) must be pre-main-sequence (PMS) clustermembers, mostly of low masses. This is a significant enlargement of theknown NGC 6530 stellar population with respect to previous opticalstudies, including Hα surveys. We identify 220 X-ray sources withcataloged stars down to V=17, while most unidentified sources havefainter counterparts. Moreover, we find an infrared counterpart in the2MASS catalog for 731 X-ray sources. The optically identified clusterX-ray sources are found in a band in the H-R diagram above the mainsequence, in the locus of 0.5-1.5 Myr PMS stars, with masses down to0.5-1.5 Msolar. We find evidence of an age gradient acrossthe field from northwest to south, suggesting a sequence of starformation events qualitatively similar to that found in earlier studiesof the same region, but differing in the details. A group of X-raysources showing frequent flares may be associated with the youngeststars in the cluster, suggesting that X-ray flaring activity isespecially intense in the youngest PMS phases of low-mass stars.
| On the Hipparcos parallaxes of O stars
We compare the absolute visual magnitude of the majority of bright Ostars in the sky as predicted from their spectral type with the absolutemagnitude calculated from their apparent magnitude and the Hipparcosparallax. We find that many stars appear to be much fainter thanexpected, up to five magnitudes. We find no evidence for a correlationbetween magnitude differences and the stellar rotational velocity assuggested for OB stars by Lamers et al. (1997, A&A, 325, L25), whosesmall sample of stars is partly included in ours. Instead, by means of asimulation we show how these differences arise naturally from the largedistances at which O stars are located, and the level of precision ofthe parallax measurements achieved by Hipparcos. Straightforwardlyderiving a distance from the Hipparcos parallax yields reliable resultsfor one or two O stars only. We discuss several types of bias reportedin the literature in connection with parallax samples (Lutz-Kelker,Malmquist) and investigate how they affect the O star sample. Inaddition, we test three absolute magnitude calibrations from theliterature (Schmidt-Kaler et al. 1982, Landolt-Börnstein; Howarth& Prinja 1989, ApJS, 69, 527; Vacca et al. 1996, ApJ, 460, 914) andfind that they are consistent with the Hipparcos measurements. AlthoughO stars conform nicely to the simulation, we notice that some B stars inthe sample of \citeauthor{La97} have a magnitude difference larger thanexpected.
| 10 MK Gas in M17 and the Rosette Nebula: X-Ray Flows in Galactic H II Regions
We present the first high spatial resolution X-ray images of twohigh-mass star forming regions, the Omega Nebula (M17) and the RosetteNebula (NGC 2237-2246), obtained with the Chandra X-Ray ObservatoryAdvanced CCD Imaging Spectrometer instrument. The massive clusterspowering these H II regions are resolved at the arcsecond level intomore than 900 (M17) and 300 (Rosette) stellar sources similar to thoseseen in closer young stellar clusters. However, we also detect softdiffuse X-ray emission on parsec scales that is spatially and spectrallydistinct from the point-source population. The diffuse emission hasluminosity LX~=3.4×1033 ergs s-1in M17 with plasma energy components at kT~=0.13 and ~=0.6 keV (1.5 and7 MK), while in Rosette it has LX~=6×1032ergs s-1 with plasma energy components at kT~=0.06 and ~=0.8keV (0.7 and 9 MK). This extended emission most likely arises from thefast O star winds thermalized either by wind-wind collisions or by atermination shock against the surrounding media. We establish that onlya small portion of the wind energy and mass appears in the observeddiffuse X-ray plasma; in these blister H II regions, we suspect thatmost of it flows without cooling into the low-density interstellarmedium. These data provide compelling observational evidence that strongwind shocks are present in H II regions.
| The total-to-selective extinction ratio determined from near IR photometry of OB stars
The paper presents an extensive list of the total to selectiveextinction ratios R calculated from the infrared magnitudes of 597 O andB stars using the extrapolation method. The IR magnitudes of these starswere taken from the literature. The IR colour excesses are determinedwith the aid of "artificial standards" - Wegner (1994). The individualand mean values of total to selective extinction ratios R differ in mostcases from the average value R=3.10 +/-0.05 - Wegner (1993) in differentOB associations. The relation between total to selective extinctionratios R determined in this paper and those calculated using the "methodof variable extinction" and the Cardelli et al. (1989) formulae isdiscussed. The R values presented in this paper can be used to determineindividual absolute magnitudes of reddened OB stars with knowntrigonometric parallaxes.
| The Massive Double-Lined O-Type Binary HD 165052
Not Available
| Molecular Hydrogen in the Lagoon: H2 Line Emission from Messier 8
The 2.12μmv=1-0 S(1) line of molecular hydrogen has been imaged inthe Hourglass region of M8. The line is emitted from a roughly bipolarregion, centred around the O7 star Herschel 36. The peak H21-0 S(1) line intensity is 8.2 ×10-15ergs-1cm-2arcsec-2. Theline centre emission velocity varies from -25kms-1 in the SElobe to +45kms-1 in the NW lobe. The distribution is similarto that of the CO J=3-2 line. The H2 line appears to beshock-excited when a bipolar outflow from Herschel 36 interacts with theambient molecular cloud. The total luminosity of all H2 linesis estimated to be ~16Lsolar and the mass of the hotmolecular gas ~9 × 10-4Msolar (without anycorrection for extinction).
| The massive double-lined O-type binary HD 165052
We present a new optical spectroscopic study of the O-type binary HD165052 based on high- and intermediate-resolution CCD observations. Were-investigated the spectral classification of the binary components,obtaining spectral types of O6.5V and O7.5V for the primary andsecondary, respectively, finding that both stars display weakCIIIλ5696 emission in their spectra. We also determined aradial-velocity orbit for HD 165052 with a period of 2.95510+/-0.00001d,and semi-amplitudes of 94.8 and 104.7+/-0.5kms-1, resultingin a mass ratio Q=0.9. From a comparison with previous radial-velocitydeterminations, we found evidence of apsidal motion in the system.Several signatures of wind-wind collision, such as phase-lockedvariability of the X-ray flux and the Struve-Sahade effect, are alsoconsidered. It was also found that the reddening in the region should benormal, in contrast with previous determinations.
| The Structure and Evolution of the Lagoon Nebula. I. Submillimeter Continuum and CO Line Mapping
We present submillimeter- and millimeter-wave maps tracing the moleculargas and dust around the edge of the H II region M8. The molecularmaterial is clumped into cores on the scale of the beam (about 0.1 pc)whose temperatures can be estimated from CO observations. The masses ofthe clumps, estimated from their continuum fluxes, are consistent with apower-law mass function with index -1.7+/-0.6, which agrees withdeterminations for other molecular clouds at similar resolutions, usingmolecular lines as tracers. The submillimeter clumps are sited at theinterface between the H II region and the background molecular cloud,where they are exposed to the ultraviolet flux of OB stars. The physicalparameters of the clumps are compared to published models of molecularclouds undergoing photoevaporation, suggesting that the pressure of theionized gas exceeds the internal pressure of the clumps and, therefore,that a shock front will be driven into the clumps. The clumps themselvescurrently appear to be gravitationally unbound, but the compression maybe sufficient to induce collapse.
| A Dozen Colliding-Wind X-Ray Binaries in the Star Cluster R136 in the 30 Doradus Region
We analyzed archival Chandra X-ray observations of the central portionof the 30 Doradus region in the Large Magellanic Cloud. The imagecontains 20 X-ray point sources with luminosities between5×1032 and 2×1035 ergs s-1(0.2-3.5 keV). A dozen sources have bright WN Wolf-Rayet or spectraltype O stars as optical counterparts. Nine of these are within ~3.4 pcof R136, the central star cluster of NGC 2070. We derive an empiricalrelation between the X-ray luminosity and the parameters for the stellarwind of the optical counterpart. The relation gives good agreement forknown colliding-wind binaries in the Milky Way Galaxy and for theidentified X-ray sources in NGC 2070. We conclude that probably allidentified X-ray sources in NGC 2070 are colliding-wind binaries andthat they are not associated with compact objects. This conclusioncontradicts earlier studies where it was argued, using ROSAT data, thattwo earlier discovered X-ray sources are accreting black hole binaries.Five of the 18 brightest stars in R136 are not visible in our X-rayobservations. These stars either are single, have low-mass companions,or have very wide orbits. The resulting binary fraction among early-typestars is then unusually high (at least 70%).
| An XMM-Newton observation of the Lagoon Nebula and the very young open cluster NGC 6530
We report the results of an XMM-Newton observation of the Lagoon Nebula(M 8). Our EPIC images of this region reveal a cluster of point sources,most of which have optical counterparts inside the very young opencluster NGC 6530. The bulk of these X-ray sources are probablyassociated with low and intermediate mass pre-main sequence stars. Oneof the sources experienced a flare-like increase of its X-ray fluxmaking it the second brightest source in M 8 after the O4 star 9 Sgr.The X-ray spectra of most of the brightest sources can be fitted withthermal plasma models with temperatures of kT ~ a few keV. Only a few ofthe X-ray selected PMS candidates are known to display Hα emissionand were previously classified as classical T Tauri stars. This suggeststhat most of the X-ray emitting PMS stars in NGC 6530 are weak-line TTauri stars. In addition to 9 Sgr, our EPIC field of view contains alsoa few early-type stars. The X-ray emission from HD 164816 is found to betypical for an O9.5 III-IV star. At least one of the known Herbig Bestars in NGC 6530 (LkHα 115) exhibits a relatively strong X-rayemission, while most of the main sequence stars of spectral type B1 andlater are not detected. We also detect (probably) diffuse X-ray emissionfrom the Hourglass Region that might reveal a hot bubble blown by thestellar wind of Herschel 36, the ionizing star of the Hourglass Region.Based on observations with XMM-Newton, an ESA Science Mission withinstruments and contributions directly funded by ESA Member states andthe USA (NASA).
| Radio Continuum and Recombination Line Study of Ultracompact H II Regions with Extended Envelopes
We have carried out 21 cm radio continuum observations of 16ultracompact H II regions using the VLA (DnC array) in a search forassociated extended emission. We have also observed the H76αrecombination line toward all the sources and the He76α line atthe positions with strong H76α line emission. The UC H II regionshave simple morphologies and large (>~10) ratios of single-dish toVLA fluxes. We detected extended emission toward all the sources. Theextended emission consists of one to several compact (~1' or 0.5-5 pc)components and a diffuse extended (2'-12' or 4-19 pc) envelope. All theUC H II regions but two are located in the compact components, where theUC H II regions always correspond to their peaks. The compact componentswith UC H II regions are usually smaller and denser than those withoutUC H II regions. For individual sources, we derive the spectral types(O7-O4) of the ionizing stars and the fractions of UV photons absorbedby dust within the nebulae, which are significantly different fromprevious estimates based on the UC H II regions alone. Our recombinationline observations show that the ultracompact, compact, and extendedcomponents have approximately the same velocity in the individualsources with one exception (G25.72+0.05), implying that they arephysically associated. The compact components in each object appear tobe ionized by separate sources, while the UC H II regions and theirassociated compact components are likely to be ionized by the samesources on the basis of the morphological relations mentioned above.This suggests that almost all of the observed UC H II regions are not``real'' UC H II regions but ultracompact cores of more extended H IIregions, and that their actual ages are much greater than theirdynamical age (<~104 yr). We find that most of simple UC HII regions previously known have large ratios of single-dish to VLAfluxes, similar to our sources. Therefore, the ``age problem'' of UC HII regions does not seem to be as serious as earlier studies argued. Wepresent a simple model in which the coexistence of the ultracompact,compact, and extended components for a long (>105 yr) time iseasily explained by combining the champagne flow model with thehierarchical structure of massive star-forming regions. The well-knownrelation between the density and diameter of H II regions,ne~D-1, is a natural consequence of thehierarchical structure according to our model. We discuss someindividual sources.
| Coordinated monitoring of the eccentric O-star binary Iota Orionis: the X-ray analysis
We analyse two ASCA observations of the highly eccentric O9 III+B1 IIIbinary Iota Orionis obtained at periastron and apastron. Based on theassumption of a strong colliding-wind shock between the stellarcomponents, we expected to see significant variation in the X-rayemission between these phases. The observations proved otherwise: theX-ray luminosities and spectral distributions were remarkably similar.The only noteworthy feature in the X-ray data was the hint of aproximity effect during periastron passage. Although this `flare' is ofrelatively low significance, it is supported by the notable proximityeffects seen in the optical, and the phasing of the X-ray and opticalevents is in very good agreement. However, other interpretations arealso possible. In view of the degradation of the SIS instrument andsource contamination in the GIS data we discuss the accuracy of theseresults, and also analyse archival ROSAT observations. We investigatewhy we do not see a clear colliding-wind signature. A simple model showsthat the wind attenuation to the expected position of the shock apex isnegligible throughout the orbit, which poses the puzzling question ofwhy the expected 1/D variation (i.e. a factor of 7.5) in the intrinsicluminosity is not seen in the data. Two scenarios are proposed: eitherthe colliding-wind emission is unexpectedly weak such that intrinsicshocks in the winds dominate the emission, or, alternatively, theemission observed is colliding-wind emission but in a more complex formthan we would naively expect. Complex hydrodynamical models are thenanalysed. Despite strongly phase-variable emission from the models, bothare consistent with the observations. We find that if the mass-lossrates of the stars are low then intrinsic wind shocks could dominate theemission. However, when we assume higher mass-loss rates of the stars,we find that the observed emission could also be consistent with apurely colliding-wind origin. A summary of the strengths and weaknessesof each interpretation is presented. To distinguish between thedifferent models X-ray observations with improved phase coverage will benecessary.
| The Search for Interstellar C60
The optical region of a number of reddened O-type stars has beenexamined on Keck I HIRES spectrograms (R=45,000) for evidence ofinterstellar C60. No absorption features were detected nearthe laboratory C60 wavelengths 3857 and 3980 Å. Aninterstellar feature is present at 6220.8 Å, but it isunacceptably far from the laboratory gas-phase wavelength of 6217.5Å. It is probably just another of the weak diffuse interstellarbands (DIBs), which are numerous in that spectral region. The mostastronomically promising C60 feature was measured in thelaboratory at 3284 Å in liquid or solid matrices. Its gas-phasewavelength can be inferred either from matrix shifts of C60features at longer wavelengths or from high-temperature gas-phasemeasurements. On that evidence, the interstellar feature could fallanywhere between about 3244 and 3306 Å. Its width is uncertain buthere is taken to be about 1 Å . No interstellar absorption fittingthese specifications and as strong as 16 mÅ has been detected inthe stars observed, including Cyg OB2/8A of E(B-V)=1.60. It follows thatin that particular line of sight and for the assumed FWHM of 1 Å ,N(C60)<4.5×1011 cm-2. However,some recent laboratory spectroscopy suggests that its width may be verymuch larger, in which case this limit would be invalid. At this upperlimit, the corresponding number of carbon atoms contained in neutralC60 indicates that that molecule would be only a minorcontributor to the total amount of C in that direction, and would beless than 1% of the amount that may be tied up in the DIBs. StrongerC60 bands are known in the laboratory at approximately 2110and 2566 Å, but the upper limit on 3284 Å suggests that theywill not be easy to detect without high resolution, high signal-to-noiseratio (S/N) satellite spectroscopy and better laboratory gas-phasewavelengths. An estimate of the column density ofC+60, under the assumption that the 9577, 9632Å bands are indeed due to C+60 and that thelaboratory f-value is correct, indicates that theC+60/C60 abundance in that line ofsight is greater than 100.
| On the Correlation between CO Absorption and Far-Ultraviolet Nonlinear Extinction toward Galactic OB Stars
A sample of 59 sight lines to reddened Galactic OB stars was examinedfor correlations of the strength of the CO Fourth Positive(A1Π-X1Σ+) absorption bandsystem with the ultraviolet interstellar extinction curve parameters. Weused archival high-dispersion NEWSIPS IUE spectra to measure the COabsorption for comparison with parametric fits of the extinction curvesfrom the literature. A strong correlation with the nonlinear far-UVcurvature term was found with greater absorption, normalized to E(B-V),being associated with more curvature. A weaker trend with the linearextinction term was also found. Mechanisms for enhancing CO in dustenvironments exhibiting high nonlinear curvature are discussed.
| Absolute proper motions of open clusters. I. Observational data
Mean proper motions and parallaxes of 205 open clusters were determinedfrom their member stars found in the Hipparcos Catalogue. 360 clusterswere searched for possible members, excluding nearby clusters withdistances D < 200 pc. Members were selected using ground basedinformation (photometry, radial velocity, proper motion, distance fromthe cluster centre) and information provided by Hipparcos (propermotion, parallax). Altogether 630 certain and 100 possible members werefound. A comparison of the Hipparcos parallaxes with photometricdistances of open clusters shows good agreement. The Hipparcos dataconfirm or reject the membership of several Cepheids in the studiedclusters. Tables 1 and 2 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| 1-m spectroscopy of normal OB stars
We have obtained spectra of 70 normal OB stars in the near-IR I(1-μm) band. The strongest features are those due to lines of thehydrogen Paschen series and neutral and ionized helium, which are, forthe most part, in absorption. The information content in this spectralrange is sufficient for only a rough classification of hot stars into`early O', `late O' and `B' types. Curiously, the leading He i tripletline, He i λ1.0830 μm, is usually not detectable, although ina few stars it is in emission; its behaviour generally correlates withthe leading helium singlet line, He i λ 2.058 μ m. These twofeatures appear to be present in emission only in stars with extremes ofmass loss or wind extension.
| Faint Emission Lines and Temperature Fluctuations in M8
We present echelle spectroscopy in the 3500-10300 Å range of theHourglass Nebula, which is embedded in the Galactic H II region M8. Thedata were obtained using the 2.1 m telescope at ObservatorioAstronómico Nacional in San Pedro Mártir, Baja California.We have measured the intensities of 274 emission lines, in particular 88permitted lines of C^+, N^0, N^+, O^0, O^+, Ne^0, S^0, S^+, Si^0, Si^+,and Si^++, some of them produced by recombination only and others mainlyby fluorescence. We have determined electron temperatures and densitiesusing different line intensity ratios. We derive the He^+, C^++, O^+,and O^++ ionic abundances as well as-for the first time in a nebularobject-the total O abundance from recombination lines; these nebularvalues are independent of the temperature structure of the nebula. Wehave also derived abundances from collisionally excited lines for alarge number of ions and elements; these abundances do depend on thetemperature structure. Accurate t^2 values have been derived bycomparing the C^++, O^+, and O^++ ionic abundances obtained making useof both collisionally excited lines and recombination lines. Acomparison of the solar, Orion Nebula, and M8 chemical abundances ismade.
| Five-colour photometry of OB-stars in the Southern Hemisphere
Observations of OB-stars, made in 1959 and 1960 at the Leiden SouthernStation near Hartebeespoortdam, South Africa, with the VBLUW photometerattached to the 90 cm light-collector, are given in this paper. They arecompared with photometry obtained by \cite[Graham (1968),]{gra68}\cite[Walraven & Walraven (1977),]{wal77} \cite[Lub & Pel(1977)]{lub77} and \cite[Van Genderen et al. (1984).]{gen84} Formulaefor the transformation of the present observations to those of\cite[Walraven & Walraven (1977)]{wal77} and \cite[Lub & Pel(1977)]{lub77} are given. Table 4 is only available in electronic format the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/Abstract.html
| Expansion and turbulence in the Hourglass region of the Lagoon Nebula (M 8). New [OIII]5007 Å line observations
We present new, seeing-limited Imaging Fabry-Perot spectroscopicobservations in the [OIII]5007 Å line in the Hourglass region ofthe Lagoon nebula. As many as 900 line profiles were obtained in aregion of 1'x1' surrounding the Hourglass, each one representing aspatial element of 2''x2''. We find expansion of the HII region and highvelocities upto -35 km s(-1) , which indicate Champagne flow. Ourobservations constrain the orientation of cavities in the Hourglassrelative to the line of sight. We identify three kinematically distinctregions in and around the Hourglass. Further, we studied turbulence inthe Hourglass region by computing the structure function using a largerset of data points at a resolution of 1''. We find a power index of 0.46for the structure function which is in variance with Kolmogoroff'stheory.
| UBV beta Database for Case-Hamburg Northern and Southern Luminous Stars
A database of photoelectric UBV beta photometry for stars listed in theCase-Hamburg northern and southern Milky Way luminous stars surveys hasbeen compiled from the original research literature. Consisting of over16,000 observations of some 7300 stars from over 500 sources, thisdatabase constitutes the most complete compilation of such photometryavailable for intrinsically luminous stars around the Galactic plane.Over 5000 stars listed in the Case-Hamburg surveys still lackfundamental photometric data.
| ICCD speckle observations of binary stars. XIX - an astrometric/spectroscopic survey of O stars
We present the results of a speckle interferometric survey made with theCHARA speckle camera and 4 m class telescopes of Galactic O-type starswith V less than 8. We can detect with the speckle camera binaries inthe angular separation range 0.035-1.5 arcsec with delta M less than 3,and we have discovered 15 binaries among 227 O-type systems. We combinedour results on visual binaries with measurements of wider pairs from theWashington Double Star Catalog and fainter pairs from the HipparcosCatalog, and we made a literature survey of the spectroscopic binariesamong the sample. We then investigated the overall binary frequency ofthe sample and the orbital characteristics of the known binaries.Binaries are common among O stars in clusters and associations but lessso among field and especially runaway stars. There are many triplesystems among the speckle binaries, and we discuss their possible rolein the ejection of stars from clusters. The period distribution of thebinaries is bimodal in log P, but we suggest that binaries with periodsof years and decades may eventually be found to fill the gap. The massratio distribution of the visual binaries increases toward lower massratios, but low mass ratio companions are rare among close,spectroscopic binaries. We present distributions of the eccentricity andlongitude of periastron for spectroscopic binaries with ellipticalorbits, and we find strong evidence of a bias in the longitude ofperiastron distribution.
| Tomographic Separation of Spectra of O-Type Binary Systems
Knowledge about the individual components of O-type binaries isdifficult to obtain because of the severe line blending present in theirspectra. An important new method is Doppler tomography, an iterativescheme that uses a set of orbital phase distributed spectra and bothradial velocity curves to reconstruct the individual component spectra(see Bagnuolo, Gies & Wiggs 1992, ApJ, 385, 708). These individualspectra can then be analyzed to determine various physical properties ofthe stars. The spectral types and luminosity classes obtained provideindicators of the temperatures and gravities. The individual projectedrotational velocities can be used to test for rotational synchronizationof the orbit or rapid spin-up due to mass transfer. For stars that arecluster members, an estimate of the magnitude difference together withthe combined absolute magnitude results in individual luminosityestimates. Finally, it is possible to search for abundance differencesdue to mass transfer or loss. Here I present results of a program ofDoppler tomography of O-binaries observed with the InternationalUltraviolet Explorer (IUE). I describe cross-correlation methods thatuse narrow-lined spectral templates to obtain precise radial velocitiesand orbital velocity curves which are used in the tomography algorithm.I present results for six systems: DH Cep, HD 165052, HD 93403, HD93205,HD 149404, and HD 152248. (SECTION: Dissertation Summaries)
| The winds of hot close binaries. Paper 3: HD 159176
Not Available
| Spectroscopic bianry orbits from ultraviolet radial velocities. Paper 26: HD 165052
Not Available
| Spectroscopic binary orbits from ultraviolet radial velocities. Paper 24: HD 167771
Not Available
| Theoretical X-ray properties of colliding stellar winds in O+O star binaries
This paper on colliding wind binaries presents a detailed andquantitative comparison between theoretical models of colliding windsand X-ray observations. We concentrate on colliding stellar winds in O+Ostar binaries. We calculate the expected X-ray spectra and orbital lightcurves, and investigate the effect of different parameters (mass-lossrate, orbital separation, system inclination, etc.) on the expectedX-ray properties. In particular we investigate three model systems; onerepresenting HD 165052 with equal winds, another representing HD 57060with very unequal winds, and a third representing an intermediate case.We demonstrate the sensitive relationship between system wind parametersand the shape of the X-ray light curve, and discuss these models inrelation to recent ROSAT results on O+O star colliding wind systems. Wefind that the variation in X-ray luminosity during the orbit isprimarily a result of varying extinction of the intrinsic X-rayluminosity by the more massive wind in the system. We also present theresults of spectral fitting to our synthetic spectra.
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| Сазвежђа: | Стрелац |
| Ректацензија: | 18h05m10.55s |
| Deклинација: | -24°23'54.8" |
| Apparent магнитуда: | 6.868 |
| Даљина: | 440.529 parsecs |
| Proper motion RA: | 2 |
| Proper motion Dec: | -2.4 |
| B-T magnitude: | 6.938 |
| V-T magnitude: | 6.874 |
Каталог и designations:
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